Volcanic Redbed-type copper mineralization in the Keshtmahaki, Southern Sanandaj-Sirjan Zone, southeastern Iran

The Keshtmahaki Cu (Ag) deposit is located in southern part of Sanandaj-Sirjan zone (SSZ), southern Iran. The host rocks are Early Cretaceous mafic to intermediate lithic tuff with NW-SE trend and discontinuous similar to 34 km extension from NW to SW of Safashahr, in which stratabound and lenticular copper orebodies distributed. The orebodies are dominated by open space filling, vein-veinlet and minor replacement, disseminated and laminated-like, and are composed predominantly of primary chalcocite, bornite, native copper, chalcopyrite and minor secondary digenite, covelite, anilite, malachite and azurite. The hypogene copper mineralization could be divided into two stages: Stage I, native copper embracement in feldspars involved in submarine volcanism, and Stage II, principal copper mineralization accompanied by propylitic alteration with quartz, calcite, epidote, sericite, hematite, chlorite and albite. The latter includes compaction and dehydration of volcano-sedimentary sequence, generation of basinal brine-related hydrothermal ore fluids and deposition of ore minerals in the lithic tuff. The ore mineralogy, alteration characteristics and sulfur isotope data provide constraints on model of the Keshtmahaki copper deposit, suggesting that the Keshtmahaki is classified as a volcanic redbed-type copper deposit formed under subaerial to shallow submarine condition during Early Cretaceous.